The invention refers to an illuminator, particularly for street lighting and industrial applications, based on a gas discharge tube which is enclosed in an outer vessel made of light transparent material, e.g. hard glass, and comprising light reflecting surfaces.
The gas discharge tubes characterized by high light efficiency and long lifetime have found many applications in street lighting and in industry. The illuminators applied for street lighting are generally arranged on the end of respective standards which extend as high as possible in order to ensure a light distribution as homogeneous as possible on a relatively long street section. This is possible by satisfying the requirement that the light distribution characteristics be shaped as a double fan. The desired characteristics can be ensured by mirrors arranged behind the light source and by horizontal or slightly declined arrangement of the illuminator axis. The illuminators of this kind can be represented e.g. by the illuminator sold under the type No. KRT-70 produced by the firm EL-CO Villamos Keszulekek es Szerelesi Anyagok Gyara (Budapest, Hungary).
To date, the illuminators applied for street lighting have light sources of significantly shorter lifetime than the housing applied for receiving the light source. This means that the housing should by capable of bearing one or more replacements of the light source.
The illuminators of that kind are exposed to the deposition of dust and other contaminants originated from the atmosphere. The deposit, which diminishes the light efficiency of the illuminator, is slowly formed on the inner and outer surfaces. An outer housing without sealing cannot improve the conditions because of the small openings and rifts which are always present. Through the openings and rifts the air can flow into the inner space of the vessel, carrying dust and other solid or aerosol particles into the inner space. The temperature conditions vary in the environment of the light source in the inner space, which results in depositing various quantities of solid or solidified components in different places.
The light crossing the housing of the known illuminators suffers high intensity loss because of the presence of two deposit layers (dust layers), at least. The dust layers on the surface of the light source and on the outer and inner surfaces of the vessel can cause a great deterioration of the light efficiency.
A further disadvantage of the known constructions follows from the fact that the light emitting and light reflecting means can be subject to a displacement during assembly and to other mechanical influencing factors. The fine adjustment of the mirrors can be deteriorated by the transport and handling of the illuminator.
It is well known to apply in the illuminator for street lighting common units for mechanical fitting and electrical connecting of the light source. For this object generally standardized threaded fittings (sockets) are applied. The threaded fittings require a relatively large space for their arrangement; sometimes the requirements of high accuracy of mechanical placing and high reliability of electrical contact are in conflict. A compromise can often be found solely by further increasing the mechanical dimensions.
It is known to prepare illuminators having an outer vessel made of hard glass. The illuminators of such kind require no outer housing because of the advantageous features of the glass. The glass can bear the intensive load of the free air applications. The problem is, however, that for realizing the required light distribution characteristics a mirror should be arranged behind the light source and this mirror is subject to different damaging influences in particular, it is practically barely protected against the atmospheric exposures. This is the reason why the mentioned illuminators lacking an outer housing but requiring outer light reflecting means have not found wide application.
The inner reflecting layers applied on the glass vessel of an illuminator are often applied in illuminators intended for use in interiors, wherein the contamination load is low. In these illuminators, however, the reflecting layers are applied in a rotational symmetry arrangement around the light emitting element (incandescent body, gas discharge tube) and the light is emitted along the longitudinal axis of the light emitting element.
In illuminators when applied for street lighting the gas discharge tubes as light sources should be arranged in a manner so as to project the direct light perpendicularly toward the mantle of the tube, and into the space to be lighted.